VDSL is the name for a transmission method, the transmission rate of which is higher than that of ADSL (Asymmetric Digital Subscriber Line). Conventionally, a VDSL system is used for a hybrid network which consists of optical fiber and copper lines, the use of optical fiber cables, in particular, providing high transmission rates.
In a hybrid network, an optical fiber cable is run up to the switching offices in the local area or even up to the cable distribution boxes on the side of the road, such conventional applications being known, for example, from the Internet address “http://www.e-online.de/sites/kom/0305237.htm.
An essential feature of digital transmission systems is an analog/digital conversion, digital transmission and subsequent digital/analog conversion of relevant data streams. In this arrangement, various methods of oversampling are conventionally used as described, for example, in the Internet reference “http://www.hoerwege.de/over+upsamp.htm.
To increase an effective bit number in conventional methods for digital data transmission, a method of noise shaping is conventionally used.
Conventional noise shaping which is used both for an A/D signal path and for a D/A signal path is described in the printed document “NORSWORTHY S R ET AL: “A programmable codec signal processor” SOLID-STATE CIRCUITS CONFERENCE, 1996. DIGEST OF TECHNICAL PAPERS. 42ND ISSCC., 1996 IEEE INTERNATIONAL SAN FRANCISCO, Calif., USA 8-10 FEB. 1996, NEW YORK, N.Y., USA, IEEE, US, 8 th Feb. 1996 (Feb. 2, 1998), pages 170-171, 438, XP010156441 ISBN: 0-7803-3136-2”.
This printed document shows that second-order noise shaping can be performed but, disadvantageously, no separate noise shaping devices are specified which could provide adapted noise shaping. In the conventional method described, it is not possible, disadvantageously, to selectively provide an allocation of noises in individual frequency bands.
Furthermore, it is not suitable that the first noise shaping provided in a first noise shaping device cannot be combined with a second noise shaping provided in a second noise shaping device.
FIG. 3 shows a circuit arrangement of a conventional analog/digital converter as used, for example, in digital transmission systems. An analog input signal 100 is supplied to an input terminal 102. The analog/digital converter 101 contains a summing device 104 and a quantizing device 111 and a digital signal 105 can be picked up as output signal at an output terminal 106, and a noise signal 113 can be connected to a second input terminal, a noise source terminal 103.
The analog input signal 100 and a noise signal 113 connected to the noise source terminal 103 are superimposed in the summing device 104, the summed signal being supplied to the quantizing device 111. The output of the quantizing device 111 is connected to the output terminal 106, a digital signal 105 being provided as the output signal.
Such analog/digital converters according to the prior art have a number of disadvantages. In VDSL systems, analog/digital converters and digital/analog converters with an effective resolution of 9 bits to 12 bits are used. The resolution of these converters influences costs and chip area and energy consumption to a high degree in a design of an integrated circuit. On the other hand, converters with a high resolution allow the complexity of external components such as duplex filters, which can be connected to the integrated circuit, to be reduced.
Thus, a balance must be struck between the costs of an integrated circuit (or of a chip area) and a complexity (thus also the costs) of external components in designing a circuit.